JPH11210928A - Burying structure of pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the increase of pipe deflection due to ground deformation, by placing a pipe with outer periphery surrounded with back-fill material on an original ground, and expanding the width of a back-fill part formed on the pipe periphery with the back-fill material from upward depth to downward depth. SOLUTION: Soil pressure applied to a back-fill part 2 due to the settling of poor ground as banking can be applied to the back-fill part 2 as a horizontal component force, using tilting of the back-fill part 2 of trapezoidal cross section. At this time, silica sand with uniform diameter as back-fill material 20 constituting the back-fill part 2 can effectively transfer the force impressed onto the tilting surface to both sides of a pipe 1 without absorbing the force in the back-fill part 2. By reducing foundation thickness, the back-fill material 20 on the lower side of the back-fill part 2 can be prevented from escaping to the original ground 3 side. Thus, by preventing soil pressure from vertically crushing the pipe 1 by the load of soil pressure from its side, excessive deformation of the pipe 1 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for burying pipes, and more particularly to a technique for burying flexible pipes such as high-density polyethylene drain pipes under embankment.

[0002]

2. Description of the Related Art High-density polyethylene drain pipes (hereinafter HD)
PE pipes) have high flexibility and follow ground deformation well, and are often buried under severe conditions that pipes of other materials cannot withstand at all. For example, in a development site that fills a valley, HDPE pipes with a diameter of 60 cm to 1 m
There are many construction examples that are buried under an embankment of 0 m. The method of burying pipes for such embankments has not been established, and there is concern about the application of the current design method for shallow burial.

It is said that the creep fracture and the buckling fracture of the HDPE tube occur at a deflection of 15%.
Moreover, considering the long-term stability of the HDPE pipe, it is necessary to suppress the maximum deflection rate at the time of embedding to about 10% in consideration of creep deformation peculiar to such a plastic pipe, that is, a decrease in the elastic modulus of polyethylene itself. There seems to be.

[0004]

However, the HDPE pipe buried in the ground receives a large load due to liquefaction of the ground due to an earthquake, land subsidence due to an increase in the level of groundwater, etc., causing a deflection that is crushed in the vertical direction, In extreme cases, the tube deforms into a heart-shaped cross section with a concave top. Such a deflection depends on the soil quality of the embankment, but about 1 m of HDPE corrugated pipe buried without any measures is backfilled by about 2 m with locally generated soil consisting of a mixture of sandy soil and cohesive soil with many fine grains. In some cases, it reached 30% at that point. Therefore, the deflection of the buried pipe is reduced by 10% as described above.
Or it is not easy to keep it below that.

[0005] By the way, the five major factors of the deformation of the buried pipe include the soil properties of the embankment material, the load, the influence of water, the type and compaction density of the backfill material, and the burial type. Therefore, the deflection of the buried pipe due to deformation of the ground can be kept within an allowable range by appropriate measures against these factors or a combination thereof.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a pipe burying structure for suppressing an increase in pipe deflection due to ground deformation by improving a burying type.

Next, a second object of the present invention is to achieve the above-mentioned desired object while minimizing the required amount of backing material necessary for adopting the above-mentioned buried type. I do.

Further, the present invention provides the above buried type,
A third object is to obtain a backing thickness that suppresses an increase in tube deflection.

A fourth object of the present invention is to reduce the change in the deformation characteristics of the backing material before and after water inundation of the ground, and to effectively exert the effect of suppressing the pipe deflection due to the above-mentioned buried type. I do.

[0010]

SUMMARY OF THE INVENTION In order to achieve the first object, the present invention provides a pipe burying structure in which a pipe is placed on an original ground with a backing material surrounding the outer circumference and buried under an embankment. Wherein the backing portion formed on the outer periphery of the pipe by the backing material is widened from an upper depth to a lower depth of the pipe.

In order to achieve the second object, the width of the backing portion at the depth of the center of the pipe is at least twice the outer diameter of the pipe.

In order to achieve the third object, the base thickness formed below the original ground and the pipe by the backing portion is made thinner than the outer diameter of the pipe.

In order to achieve the fourth object, the backing material is a ground material having a low fine particle content.

[0014]

According to the first aspect of the present invention, the earth pressure applied to the backing portion due to the settlement of the embankment is increased in the horizontal direction by using the inclination of the backing portion which is widened from the upper depth to the lower depth of the pipe. Can be transmitted to both sides of the tube via the backing portion, and can act as a force against the vertical crushing force of the tube.

Further, according to the configuration of the second aspect, the deflection of the pipe can be kept within an allowable range with a minimum necessary backing amount.

Further, according to the third aspect of the invention, the backing portion is prevented from being displaced downward on both sides of the pipe due to the settlement of the embankment, and the horizontal component of the earth pressure is effectively applied to both sides of the pipe. be able to.

According to the fourth aspect of the present invention, the rate of decrease in the deformation coefficient of the backing material due to flooding of the embankment can be reduced, and the deformation coefficient of the backing material after flooding can be maintained large. Therefore, the horizontal component of the earth pressure accompanying the settlement can be uniformly transmitted to the pipe through the backing portion.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a buried structure of a pipe to which the present invention is applied. As shown in FIG.
The pipe 1 made of a PE pipe is placed on the original ground 3 around the outer periphery by a backing material 20 and buried under the embankment 4. Then, according to the present invention, the backing portion 2 formed on the outer periphery of the pipe by the backing material 20 is widened from the upper depth to the lower depth of the pipe 1. In this embodiment, the backing portion 2 has a trapezoidal cross section, and the angle between the lower base of the trapezoid and the two oblique sides is 45 ° symmetrically.

FIG. 2 shows such a buried type according to the present invention,
In comparison with other buried types, the deformation mechanism is shown schematically. In the type without backfilling as shown in (A) of the figure, the horizontal force of earth pressure accompanying ground subsidence ( (Indicated by black arrows in the figure) is small, so that the vertical crushing deformation of the pipe becomes large. On the other hand, in the case of the backfilling of the inverted trapezoidal cross section as shown in FIG. 3 (B), the action of the earth pressure in the horizontal direction is larger than in the case where backfilling is not performed. The movement of the soil (knitted arrow in the figure) causes the backing portions on both sides of the pipe to slip outward (the boundary of the shift is shown by a dotted line in the figure), and the horizontal force is released. On the other hand, in the form shown in FIG. 3C according to the present invention, the horizontal component of the earth pressure generated by the movement of the embankment can be effectively applied to both sides of the pipe.

FIG. 3 shows the relationship between the above three embedding types and the deformation rate. In the case where backfilling is not performed as shown in FIG. If the reverse trapezoidal cross section as shown in FIG. 2B is backfilled as shown in FIG. 2B, the deformation ratio δmax value is 15% of the deformation ratio δmax value, which is far more than 15%. In the form shown in FIG. 2 (C) according to the invention, the allowable value δ =
It can be seen that the deformation ratio can be kept within the allowable deformation rate of 7%.

Next, as shown in FIG. 1, the backing portion 2 has a backing width Bs at the center depth of the pipe that is twice the outer diameter D of the pipe. FIG. 4 shows the difference in the deformation mechanism depending on the size of the backing width Bs. It can be seen that the larger the backing width Bs, the greater the resistance of the soil. FIG. 5 shows the relationship between the backing width Bs and the deformation rate of the pipe 1, and the ratio Bs of the backing width to the pipe outer diameter.
If / D is less than 2, the allowable value δ exceeds 7%,
It is understood that by setting Bs / D to 2 or more, the allowable value δ can be suppressed to 7% or less. When the value of Bs / D is 2 or more, a decrease in the deformation rate can be seen by increasing this value, but the decrease in the deformation rate with respect to the increase in Bs / D gradually decreases. Therefore, in this embodiment, twice the tube outer diameter D is selected as the minimum necessary backing width Bs.

The base thickness Hb formed below the original ground 3 and the pipe 1 by the backing portion 2 is sufficiently thinner than the pipe outer diameter D as shown in FIG. , 0.22 times the pipe outer diameter D. FIG. 6 shows the difference in the deformation mechanism according to the magnitude of the base thickness Hb.
If b is too large, the backing material 20 is deformed to be shifted downward on both sides of the pipe 1, so that the resistance of the soil applied to the pipe is reduced. Accordingly, as shown in FIG. 7, the relationship between the base thickness Hb and the deformation rate δ is shown. When the ratio Hb / D of the base thickness to the pipe outer diameter is 0.6 or more, the deformation rate δ becomes 7% or more of the allowable value. When the value is less than the above, it can be seen that although the deformation ratio δ decreases, the decrease in the deformation ratio δ with respect to the decrease in Hb / D gradually decreases. On the other hand, the upper bottom of the backing portion 2 is located in contact with the outer periphery of the pipe 1 as shown in FIG. This is because the backing thickness above the pipe does not significantly affect the improvement of the deformation rate δ of the pipe, so that the backing thickness is set to the minimum necessary.

The backing material 20 is a ground material made of sand or crushed stone having a low fine particle content.
Silica sand is used. FIG. 8 shows the passing weight percentage of silty sand, Masato and quartz sand. In the case of silty sand (shown by a solid line in the figure) and Masato (also shown by a dashed line), the maximum particle size is 2.0 mm. In the case of silica sand (indicated by a broken line in the figure), the maximum particle size is about 1.4 mm and does not include fine particles. You can see that.

As described above, in the case of the backing material such as silica sand having a relatively large particle size, the reduction rate of the deformation coefficient of the backing material due to water erosion is reduced, and the backing material after water immersion is reduced. Since the deformation coefficient can be kept large, the horizontal component of the earth pressure accompanying the land subsidence can be uniformly transmitted to the pipe through the backing portion.

As described in detail above, according to the above embodiment, the earth pressure applied to the backing portion 2 due to the subsidence of the soft ground as the embankment is obtained by utilizing the inclination of the backing portion 2 having a trapezoidal cross section. ,
The component force in the horizontal direction can act on the backing portion 2. At this time, silica sand having a uniform particle size as the backing material 20 constituting the backing portion 2 applies the force applied to the inclined surface to the backing portion 2.
It can be effectively transmitted to both sides of the tube 1 without being absorbed inside. Further, by reducing the base thickness Hb, it is possible to prevent the backing material 20 below the backing portion 2 from escaping to the original ground 3 side. Thus, according to the configuration of the above-described embodiment, the vertical deformation of the pipe 1 due to the earth pressure can be prevented by the load of the earth pressure from the side, and the excessive deformation of the pipe 1 can be prevented.

Although the present invention has been described in detail based on one embodiment in which the present invention is applied to a specific HDPE pipe, the present invention can be widely applied to pipes of other materials.

[0027]

According to the structure of the first aspect of the present invention, the inclination of the backing portion is such that the earth pressure applied to the backing portion due to the settlement of the embankment is increased from the upper depth to the lower depth of the pipe. Utilizing this, it can be transmitted as a horizontal component to both sides of the pipe through the backing and act as soil resistance against crushing in the vertical direction of the pipe, thereby reducing the deflection of the pipe. Can be reduced.

Next, according to the configuration of the second aspect, the deformation of the pipe can be kept within a permissible range that does not cause breakage with the minimum necessary backfill.

According to the third aspect of the present invention, the backing portion is prevented from being displaced downward on both sides of the pipe due to the settlement of the embankment, and the horizontal component of the earth pressure is effectively reduced on both sides of the pipe. To reduce the vertical deflection of the tube. Moreover, since the backing thickness can be reduced, the amount of backing material used can be reduced.

According to the structure of the fourth aspect,
The earth pressure accompanying the settlement of the embankment can be uniformly transmitted to the pipe through the backing part. In addition, it is possible to suppress a change in the transmission characteristic of the earth pressure due to the repetition of the embankment settlement.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a pipe burying structure according to the present invention.

FIG. 2 is a schematic cross-sectional view showing a deformation mechanism by comparing the pipe burying structure of the embodiment with another burying type.

FIG. 3 is a graph showing a relationship between an embedding type and a deformation rate.

FIG. 4 is a schematic cross-sectional view showing a difference in a deformation mechanism depending on a backing width.

FIG. 5 is a graph showing the relationship between the backing width and the deformation ratio.

FIG. 6 is a schematic sectional view showing a difference in a deformation mechanism depending on a base thickness.

FIG. 7 is a graph showing a relationship between a base thickness and a deformation rate.

FIG. 8 is a graph showing the fine particle content of each backing material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pipe 2 Backing part 3 Original ground 4 Embankment 20 Backing material

Claims (4)

[Claims] In a buried structure of a pipe in which a pipe is placed on the original ground around an outer periphery by a backing material and buried under an embankment, a backing part formed on the outer periphery of the pipe by the backing material is provided. A buried pipe structure characterized by being widened from an upper depth to a lower depth. 2. The buried structure for a pipe according to claim 1, wherein the width of the backing portion at the center depth of the pipe is at least twice the outer diameter of the pipe. 3. The buried pipe structure according to claim 1, wherein a base thickness formed below the original ground and the pipe by the backing portion is made thinner than an outer diameter of the pipe. 4. The pipe burying structure according to claim 1, wherein the backing material is a ground material having a low fine particle content.